Plasma CVD film-forming device

ABSTRACT

A plasma CVD film-forming device forms a film on a semiconductor substrate in such as way that the film quality and film thickness of a thin film becomes uniform. The plasma CVD film-forming device to form a thin film on a semiconductor substrate includes a vacuum chamber, a showerhead positioned within the vacuum chamber, and a susceptor positioned substantially in parallel to and facing the showerhead within the vacuum chamber and on which susceptor the object to be processed is loaded and the central part of the showerhead and/or the susceptor constitutes a concave surface electrode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a device for forming a thin film on asemiconductor substrate by the vapor growth method using plasma, andparticularly it relates to a semiconductor processing device that ischaracterized by the shape of a showerhead and/or a susceptor.

2. Description of the Related Art

FIG. 1 outlines a conventional parallel-flat-plate type plasma CVDfilm-forming device. The conventional plasma CVD film-forming devicecomprises a vacuum chamber 1, a showerhead 2 positioned upright withinthe vacuum chamber substantially horizontally and a susceptor 3positioned substantially in parallel and facing the showerhead withinthe vacuum chamber 1.

In the vacuum chamber 1, an exhaust port 5 leading to a vacuum pump (notshown) is used for vacuum exhausting the inside of the chamber.

At the base of the showerhead 2, multiple fine holes 11 for emitting ajet of material gas are positioned. The showerhead 2 is also linked to amaterial gas supply tank 6 through a line 10. On the line 10, a massflow controller 8 for controlling a flow of the material gas ispositioned. An RF power source 4 is also electrically connected to theshowerhead 2, and functions as one side of the electrodes.

The susceptor 3 is normally an aluminum column within which a heater 14is embedded. The susceptor 3 is supported by a support 12 and can bealso rotated, for example, by a rotating mechanism. The susceptor 3 isalso connected to ground 13 and functions as the other electrode. On thesurface of the susceptor 3, a semiconductor substrate 9 is loaded and isfixed by vacuum fastening, etc.

Operation of the conventional plasma CVD film-forming device isexplained below.

First, gas within the chamber 1 is vacuum exhausted by the vacuum pumpfrom the exhaust port 5, and preferably a low pressure is maintainedwithin the chamber 1.

Next, a preselected material gas flowing from the material gas supplytank 6 is controlled by the mass flow controller 8 at a preferable flow.A material gas controlled at a preferable flow is transported to theshowerhead 2 through the line 10 and is jetted out from the multiplefine holes 11 provided at the base, toward the semiconductor substrate.

After a flow is stabilized, a radio-frequency (RF) electric field isgenerated between the showerhead connected to the RF power source andthe susceptor 3 grounded to the earth 13. The above-mentioned materialgas within the chamber 1 is ionized and a plasma state occurs. Atoms ofthe ionized material gas show a chemical reaction at a reaction regionon the semiconductor substrate, and a desirable thin film is formed onthe semiconductor substrate.

As a material gas, silicon source gasses such as SiH₄,DM-DMOS[(CH₃)₂Si(OCH₃)₂] and TEOS, fluorine source gasses such as C₂F₆,oxidizing gasses such as oxygen and inert gasses such as Ar or He can beused.

The type and quality of a film formed on the surface of thesemiconductor substrate 9 change according to the type, flow andtemperature of the material gas, the RF frequency type, and the plasma'sspatial evenness.

SUMMARY OF THE INVENTION

The evenness of a film formed on the semiconductor substrate and theevenness of plasma density at the reaction region are closely related.As shown in FIG. 1, a distance between the susceptor 3 and theshowerhead 2, i.e., a distance between the semiconductor substrate 9 andthe showerhead 2, is fixed for a conventional plasma CVD film-formingdevice. In general, in the parallel-flat-plate type plasma CVDfilm-forming device, an electric field intensity distribution generatedbetween two plane electrodes (Ø250 mm) has the property of beingstrongest at the center and gradually weakening toward the outer edgealong a radius. In the film-forming region of a semiconductor substrateof Ø200 mm, the intensity distribution is approximately ±5%.Consequently, the electric field around the center of the semiconductorsubstrate 9 is relatively stronger than the electric field toward theouter edge along the radius, and the plasma density is also higher andthe reaction of a material gas becomes more active. As a result, a thinfilm formed becomes thicker at the center, and the film quality becomesuneven at the center and at the outer area of the center.

This problem conventionally has been dealt with by controlling the flowor mixing ratio of gas supplied, the value of RF frequency applied andRF power energy. However, when these parameters are changed, the qualityof the generated film and the film-forming speed change and stability ofthe process deteriorates. Particularly, if the mixing ratio and the flowof a material gas considerably affect the film quality, this problembecomes more serious.

It is important to resolve the problem of the evenness of a film due tothe need for a larger diameter for semiconductor substrates in thefuture.

Consequently, an object of this invention is to provide a plasma CVDfilm-forming device that forms a thin film with an even film quality andan even film thickness on a semiconductor substrate.

Other object of this invention is to provide a plasma CVD film-formingdevice that is a thin film with an even film quality and thickness for asubstrate with a diameter of more 300 mm.

Another object of this invention is further to provide a plasma CVDfilm-forming device at a low manufacturing cost and with a simpleconfiguration.

To accomplish the above-mentioned objects, a plasma CVD film-formingdevice according to this invention comprises the following means:

A plasma CVD film-forming device for forming a thin film on a substrate,comprises: (a) a vacuum chamber; (b) a showerhead positioned within saidvacuum chamber; and (c) a susceptor positioned substantially in parallelto and facing said showerhead within said vacuum chamber and on whichsaid substrate is loaded, wherein the showerhead and the susceptor areused as electrodes and have surfaces facing each other, at least one ofwhich surfaces is concave.

In the above, in an embodiment, the concave surface is a rotatablysymmetrical surface around an axis of the showerhead or the susceptor.

In another embodiment, a distance between said showerhead and saidsusceptor satisfies the following relation:

 fd=|dc−da|/da×100 fd=1%˜100%

wherein:

fd is a deformation ratio of the central part of said showerhead'ssurface that faces said substrate,

da is the average distance between said showerhead and said susceptor atan outer perimeter position of said substrate,

dc is the average distance between said showerhead and said susceptor ata point on a radius of a distance equivalent to da from the center ofsaid substrate.

Further, in yet another embodiment, a distance between said showerheadand said susceptor satisfies the following relation:

fd′=|dc′−da′|/da′×100 fd′=1%˜100%

wherein:

fd′ is a deformation ratio of the central part of said susceptor'ssurface that faces said substrate,

da′ is the average distance between said showerhead and said susceptorat an outer perimeter position of said substrate,

dc′ is the average distance between said showerhead and said susceptorat a point on a radius of a distance equivalent to da′ from the centerof said substrate.

In an embodiment, a distance between the showerhead and the susceptorbecomes greater toward the center and it becomes greatest at the center.

In the above, deformation ratios fd and fd′ can range from 1%˜100%independently or concurrently. In an embodiment, deformation ratio fd orfd′ is 5-35%.

Deformation ratio fd or fd′ may be determined to render substantiallyuniform a distribution of electric field intensity over the substratewhile forming a film thereon.

In the above, distance da or da′ may be in the range of 3 to 300 mm,preferably 5 to 100 mm. Difference |dc−da|or|dc′−da′| may be in therange of 0.3 to 50 mm, preferably 0.5 to 20 mm.

Deformation ratio fd or fd′ can be indicative of uniformity of qualityand thickness of a film formed on a substrate. Additionally, a distance,dw, between the susceptor and the substrate can be indicative of qualityand uniformity of thickness of a film and may be in the range of 0.1 to10 mm, preferably 0.1 to 5 mm.

In an embodiment, the susceptor can have a diameter sufficient tosupport a substrate having a diameter of 300 mm or larger. A film can beformed on a large substrate.

Other conditions for processing a substrate can be the same as thoseconventionally employed. The showerhead may supply a material gascontaining a compound selected from the group consisting of compoundswhich can be expressed by Si_(x)O_(y)C_(z)N₁H_(m), wherein x, y, z, l,and m are independently zero or an integer, including SiH₄, Si(OC₂H₅)₄,(CH₃)₂Si(OCH₃)₂, and C₆H₆. To the material gas, an additive gas such asHe and O₂ may be added in an embodiment. A radiofrequency power may beapplied between the showerhead and the susceptor. Further, the susceptormay comprise a heater.

The present invention also relates to a method for forming a thin filmon a substrate by using the aforesaid plasma CVD film-forming device.The method may comprise: (I) loading a substrate on the susceptor; (ii)controlling the atmosphere in the vacuum chamber; (iii) applying energybetween the showerhead and the susceptor; and (iv) forming a thin filmon the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 roughly illustrates a conventional plasma CVD film-formingdevice.

FIG. 2 shows a first example of the plasma CVD film-forming device thatpossesses a showerhead according to this invention.

FIGS. 3a, 3 b, and 3 c show variation examples of a showerhead accordingto this invention.

FIG. 4 shows a second example of the plasma CVD film-forming deviceaccording to this invention.

FIG. 5 shows a third example of the plasma CVD film-forming deviceaccording to this invention.

FIG. 6 is a graph showing the relation of the surface depth and adistance from the electrode center according to the difference in theshowerhead lower surface shape.

FIG. 7 is a graph showing the relation of the degree of concavity at thecentral part of the electrode and the film thickness of thesemiconductor substrate center.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

This invention is explained referring to the following figures:

FIG. 2 roughly illustrates the first example according to thisinvention. The same symbols are used for the same materials used in FIG.1. The first example of a plasma CVD film-forming device for forming athin film on an object to be processed according to this inventioncomprises a vacuum chamber 1, a showerhead 20 positioned within saidvacuum chamber and a susceptor 3 positioned substantially in parallel toand facing said showerhead within said vacuum chamber and on whichsusceptor said object to be processed is loaded. This example shows acase where a distance between said showerhead and said susceptor becomesgreater toward the center and it becomes the greatest at the center.

The plasma CVD film-forming device shown in FIG. 2 operates in the sameway as the conventional plasma CVD film-forming device shown in FIG. 1.However, in this invention, by transforming the surface shape ofelectrodes, distribution of an electric field within the surface isimproved and the evenness o film to be formed is improved.

Preferably, a base 21 of the showerhead 20 comprises a concave rotatingsurface. Here, a rotating surface is defined as a curved surface that isgenerated by rotating a curved line on a plane around a straight line onthe same plane.

In FIG. 2, a distance between the showerhead 20, i.e., an upperelectrode, and the semiconductor substrate 9 is the greatest at thecentral point 22 and gradually lessens toward the outer edge along aradius.

The deformation ratio fd of the center 24 of the upper electrode 21 isdefined as follows:

fd=|dc−da|/da×100 fd=1%˜100%

wherein:

fd is a deformation ratio of the central part 24 of the surface of theshowerhead 20, which faces the semiconductor substrate 9,

da is the average distance between the showerhead 20 and the susceptor 3at an outer perimeter position 23 of the semiconductor substrate 9,

dc is the average distance between the showerhead 20 and the susceptor 3at a point on a radius of a distance equivalent to da from the center 22of the semiconductor substrate 9. A deformation ratio fd according tothis invention is fd=1%˜100%,

preferably 5˜35%. The deformation ratio fd differs according to the typeof reaction gas supplied, the mixing ratio, the RF power applied, andother factors, and the most suitable value is selected.

FIG. 3 shows variation[ example]s of the above-mentioned first exampleof this invention. In the first variation example shown in FIG. 3(a),the base of the showerhead 20 comprises a rotating surface whose partfacing the semiconductor substrate is largely concave with its center 24a protruding. In the second variation example shown in FIG. 3(b), thebase of the showerhead 20 b is concave in a substantially conical shapeand its center 24 b protrudes. In the third variation example shown inFIG. 3(c), the base of the showerhead 20 c has two concave parts and thecenter 24 c is nearly flat.

Thus, the structure of the showerhead 20 of this invention is notrestricted to the one shown in the first example, for which a distancebetween the showerhead 20 and the susceptor 3 becomes greatest at thecenter. In other words, the structure of the showerhead according tothis invention is substantially characterized in the regard that thepart facing the semiconductor substrate is concave, and for that concavestructure, the most suitable one is selected according to thespecifications of the showerhead and the susceptor, the RF power, andother film-forming conditions.

FIG. 4 roughly illustrates the second example of this invention. Thisworks in the same as a conventional plasma CVD film-forming device, butin this second example, the surface 31 of the susceptor 30 comprises aconcave rotating surface. The showerhead 2 is the same flat-typeshowerhead and constitutes the upper electrode. The distance between thesusceptor 30, i.e., the lower electrode, and the showerhead 2 isgreatest at the central point 33 and gradually lessens toward the outeredge along a radius. The semiconductor substrate 9 contacts thesusceptor solely at its rim 32, and it can be fixed by, for example,vacuum fastening.

The deformation ratio fd′ of the central part of the lower electrode 30is defined as follows:

fd′=|dc′−da′|/da′×100

wherein:

fd′ is the deformation ratio of the central part of the surface of thesusceptor 30, which faces the semiconductor substrate 9,

da′ is the average distance between the showerhead 2 and the susceptor30 at the outer perimeter position 34 of the semiconductor substrate 9,

dc′ is the average distance between the showerhead 20 and the susceptor30 at a point on a radius of a distance equivalent to da′ part from thecenter 22 of the semiconductor substrate 9. The deformation ratio fd′according to this invention is fd′=1˜100%, preferably 5˜35%. Thedeformation ratio fd′ differs according to the type and mixing ratio ofreaction gas, the RF power applied, and other factors, and the mostsuitable value is selected.

At this point it should be noted that a variation example similar to thevariation example of the first example shown in FIG. 3 is applicable tothe susceptor 30 of this invention. In other words, the structure of thesusceptor 30 of this invention is not restricted to those shown in thesecond example, for which the distance between the showerhead and thesusceptor becomes greatest at the central part.

Next, the third example of this invention is roughly illustrated in FIG.5. This works in the same way as a conventional plasma CVD film-formingdevice, but in the third example, the respective surfaces 21 and 31 ofthe showerhead 20 and the susceptor 30 comprise concave rotatingsurfaces. The showerhead 20 has the same rotating surface 21, which isconcave at the center, as that of the first example and it constitutesthe upper electrode. Similarly to the second example, the susceptor 30comprises a rotating surface that is concave at the center. The distancebetween the susceptor 30 and the showerhead 20 is greatest betweenrespective central points 33 and 24 and it gradually lessens toward theouter edge along a radius. The semiconductor substrate 9 contacts thesusceptor only at its rim 32 and is fixed by, for example, vacuumfastening.

The deformation ratio fd for the third example according to thisinvention is fd=1˜100%, preferably 5˜35% (in another embodiment,fd=10˜35%). The deformation ratio fd differs according to the type andmixing ratio of reaction gas, the RF power applied, and other factors,and the most suitable value is selected.

EXAMPLE

The experimental results of this invention are explained below.

The experiment intends to measure each film thickness distributionobtained using two types of showerheads according to the first exampleof this invention.

FIG. 6 is a graph showing the shape of the surface of each showerhead.Rotating surfaces on the showerhead base are formed by rotating therespective shapes a and b on the central axis of the electrode used as arotating axis. As a result, a difference results in the electrodeinterval toward the radius.

The experiment was conducted under the following conditions:

Distance da between the electrodes at the outer rim of the semiconductorsubstrate=10 mm

The depth of the concave surface at the center 24 of the showerhead a(the degree of concavity)=1 mm, deformation ratio fd=11%

The depth of the concave surface at the center 24 of the showerhead b(the degree of concavity)=3 mm, deformation ratio fd=32%

Ø of the semiconductor substrate used=200 mm

Temperature at the lower electrode=400° C. (752° F.)

Frequency f of RF power source used=13.56 MHz

Material gas=DM-DMOS, flow=20 sccm

Material gas=Ar, flow=10 sccm

Material gas=He, flow=10 sccm

From the experimental results shown in FIG. 7, while the film thicknessaccumulated on the semiconductor substrate around the central part ofthe showerhead electrode was approximately 6% thicker for a conventionalparallel-flat-plate type plasma CVD film-forming device than the averagefilm thickness, the film thickness accumulated on the semiconductorsubstrate around the central part of the showerhead according to thisinvention was improved to remain 1.5% thicker than the average filmthickness and the film thickness of a thin film accumulated on thesemiconductor substrate around the central part of the showerhead bresulted conversely in a 2.5% thinner than [the] average film thickness.

From these experimental results, it was found that the evenness of afilm could be improved by forming electrodes so that the distancebetween the electrodes becomes greater around the central part of thesemiconductor substrate, thereby adjusting the plasma electric field toevenly distribute its intensity.

Alternatively, the direction of thermal expansion of the electrodes whenforming a film on the semiconductor substrate changes in the directionof narrowing the electrode interval, or conversely, in the direction ofwidening it according to a method of fixing the outer perimeter ofelectrodes, residual stress of an electrode surface, subtle deflectionof a surface shape or a shape of a fine hole for supplying reaction gas,etc.

Conventionally, it was difficult to control changes in this direction tobe constant at all times. If the distance between the electrodes isshortened, the electric field around the central part of thesemiconductor substrate becomes very strong, the growth rate of the filmalso increases and the evenness of the film deteriorates.

However, according to this invention, by making the structure of thecentral part concave from the beginning, the evenness of the film aroundthe semiconductor substrate center further improves because theelectrodes expand only in the direction of widening the electrodeinterval.

Effects of the Invention

With an embodiment of the plasma CVD film-forming device according tothis invention, it has become possible to form a thin film on asemiconductor substrate evenly. As a result, demand for more highlyintegrated and higher performance semiconductor elements can beaddressed.

Moreover, with an embodiment of the plasma CVD film-forming deviceaccording to this invention, demand for more even and stable filmthickness and film quality can be addressed.

Furthermore, an embodiment of the plasma CVD film-forming deviceaccording to this invention makes it possible to sufficiently address alarger diameter of future semiconductor substrates and to form a thinfilm evenly across a wide area.

It will be understood by those of skill in the art that numerous andvarious modifications can be made without departing from the spirit ofthe present invention. Therefore, it should be clearly understood thatthe forms of the present invention are illustrative only and are notintended to limit the scope of the present invention.

What is claimed is:
 1. A plasma CVD film-forming for forming a tin filmon a flat substrate, which comprises: a vacuum chamber; a showerheadpositioned within said vacuum chamber, from which a reaction gas isdischarged substantially uniformly with respect to its surface; and asusceptor positioned substantially in parallel to and facing saidshowerhead within said vacuum chamber, wherein the surface of saidshowerhead is concave, and a distance between said showerhead and saidsusceptor satisfies the following relation: fd=dc−da|/da×100 fd=1%-100%wherein: fd is a deformation ratio of the central part of saidshowerhead's surface that faces said substrate, da is the averagedistance between said showerhead and a plane defined by an outerperimeter position of said susceptor, dc is the average distance betweensaid showerhead and said plane at a point on a radius of a distanceequivalent to da from the center of said plane, wherein fd is configuredto render substantially uniform a distribution of electric filedintensity over the flat substrate while forming a film thereon, whereinthe surface of said susceptor is concave, and a distance between saidshowerhead and said susceptor satisfies the following relation:fd′=|dc′−da′|/da′×100 fd′=1%-100% wherein: fd′ is a deformation ratio ofthe central part of said susceptor's surface that faces said substrate,da′ is the average distance between said susceptor and a plane definedby an outer perimeter position of said showerhead, dc′ is the averagedistance between said susceptor and said plane at a point on a radius ofa distance equivalent to da′ from the center of said plane, wherein fd′is configured to render substantially uniform a distribution of electricfiled intensity over the flat substrate while forming a film thereon,and the substrate contacts said susceptor only at a lower rim of thesubstrate while forming the film, and the substrate remainssubstantially flat during the process.
 2. The plasma CVD film-formingdevice according to claim 1, wherein the concave surface of theshowerhead is a rotatably symmetrical surface around an axis of theshowerhead.
 3. The plasma CVD film-forming device according to claim 1,wherein deformation ratio fd is 5-35%.
 4. The plasma CVD film-formingdevice according to claim 1, wherein distance da is in the range of 3 to300 mm.
 5. The plasma CVD film-forming device according to claim 1,wherein distance dc is in the range of 3.3 to 350 mm.
 6. The plasma CVDfilm-forming device according to claim 1, wherein deformation ratio fd′is 5−35%.
 7. The plasma CVD film-forming device according to claim 1,wherein distance da′ is in the range of 3 to 300 mm.
 8. The plasma CVDfilm-forming device according to claim 1, wherein distance dc′ is in therange of 3.3 to 350 mm.
 9. The plasma CVD film-forming device accordingto claim 1, wherein the concave surface of the susceptor is a rotatablysymmetrical surface around an axis of the susceptor.
 10. The plasma CVDfilm-forming device according to claim 1, wherein the showerheadsupplies a material gas containing a compound selected from the groupconsisting of compounds which can be expressed bySi_(x)O_(y)C_(z)N₁H_(m), wherein x, y, z, l, and m are independentlyzero or an integer, including SiH₄, Si(OC₂H₅)₄, (CH₃)₂Si(OCH₃)₂, andC₆H₆.
 11. The plasma CVD film-forming device according to claim 1,wherein the susceptor has a diameter sufficient to support a substratehaving a diameter of 300 mm or larger.
 12. The plasma CVD film-formingdevice according to claim 1, wherein an radiofrequency power is appliedbetween the showerhead and the susceptor.
 13. The plasma CVDfilm-forming device according to claim 1, wherein the susceptorcomprises a heater.